Method for the deburring of zinc-base die castings



Oct. 4, 1960 1 NEWELL Erm. 2,955,027

METHOD FOR THE DEBURRING OF ZINCBSE DIE CASTINGS Filed Aug. v, 1957 INVENTOR 15mm: I mr 'View ETTIES H LLluler-l United States Patent O METHOD FOR THE DEBURRING F ZINC-BASE DIE CASTINGS Isaac L. Newell, 209 Brimlield Road, Wethersfield, Conn.,

and Ernest A. Walen, 222 Farmington Road, Longmeadow, Mass.

Filed Aug. 7, 1957, Ser. No. 676,854

6 Claims. (Cl. il- 42) The present invention relates to improved methods of deburring zinc die cast parts by means of chemical action on the metal.

Cleaning and deburring of zinc die cast parts has always presented a special problem because of the varied shapes of the parts and particularly since many die castings have recessed areas or small holes. Chips result from drilling or threading operations, also burrs are raised in these operations aswell as in punching and grinding operations. These burrs and chips as well as the flash from the molding operation are generally required to be removed from the casting by a cleaning operation. Such cleaning and met-al removal has long been accomplished by hand operations with abrasive wheels or belts. Many parts require hand service when holes or surface areas are difficult to reach with mechanical or motor-operated tools. Such operations are not only very time consuming and expensive, but, in addition, are not always satisfactory. In fact it is impossible economically to mechanically clean die casting parts which contain hidden holes.

We have discovered a new and novel method for cleaning and deburring intricate die castings chemically, the method being neither expensive nor time consuming. Our method consists essentially in simply immersing the die casting in an acid oxidizing solution containing activators and inhibitors which will cause attack on the sharp edged parts and remove them without excessive attack on other surfaces of the die casting. The sharp edges of chips will also be attacked and because of the number of sharp edges on the chips they will either be completely eaten away or so reduced in size that they will readily fall from the casting.

We have found that an acid bath containing chromate ions, nitrate ions, at least one ion from the group of weak acids consisting of boric acid and monocarboxylicaliphatic acid, having not more than 4 carbon atoms, at least one ion taken from the group of uorine compounds consisting of uorides, uoborates and fluosilicates and at least one ion taken `from the group of strong mineral acid ions consisting of sulphates, phosphates and sulfamates is satisfactory for deburring a common zinc-base die casting alloy covered by ASTM specification B86-48 as alloy XXIII and having the composition given, for commercial purposes, below in Table I. This alloy is also widely known under the trade name Zamak 3 but will hereinafter be referred to merely as alloy XXIII.

When hydrochloric acid is added to the above bath, it will also be found satisfactory for the deburring of high copper zinc-base alloy covered by ASTM specification B86-48 as alloy XXV and having the composition also given in Table I. This alloy is also widely known under ICC the trade name Zamak 5 but will hereinafter be referred to merely as alloy XXV.

From the above it will be apparent that the object of the invention is to provide improved methods for removing burrs, chips, -ash and the like from zinc-base die castings. The manner in which this object is attained may be ascertained by a reading of the following specification containing exemplary examples of how the invention may be successfully practiced and the particular novelty thereof pointed out in the appended claims.

The accompanying drawing has a single ligure depicting the approximate form which a burr may take on a zinc die cast part and then, in dotted lines, the approximate form of the part after being treated in accordance with the methods disclosed herein.

Chemical deburring in accordance with ythe present invention can take place with bath temperatures as low as 60 F. and as high as 165 F. and the time for satisfactory deburring will depend to a large extent on the size and character of the burrs to be removed. We have found that some parts may be deburred in a few seconds whereas others may take as long as l0 minutes. The chemical actiontakes place on all exposed surfaces of the parts, but this chemical action is faster on sharp edges than on fiat surfaces. Thus the bulk of the attack is on the burrs, however, some attack occurs on the flat surfaces and therefore the immersion time must be restricted, depending upon the amount of attack that can be allowed on sections other than the burrs.

A typical operation for the deburring of a zinc-base die casting would be as follows:

(l) Soak clean in a conventional cleaner for zinc to remove oil and grease and loosen dirt and metal particles.

(2) Rinse in water.

(3) Deburr `in the appropriate acid oxidizing solution as taught herein.

(4) Rinse in water to remove the acid.

(5) Dry the part or continue with other treatments such as plating or conversion coatings as desired.

While the above typical cycle indicates dipping or immersion of the part in the acid bath, there is no reason that this composition could not be used for spraying parts for the removal of burrs and flash. This is especially useful where selective metal removal is desired. 'The following Table II gives l5 examples of solutions which we have found to be suitable for use in the deburring of the two most common types of zinc-base die casting alloys XXIII and XXV.

TABLE II Solution No 1 2 3 4 5 6 ChromlcAcid 350 270 270 Nitric Acid 80 150 115 115 97 Formic A f-id 65 .Aoetic Avid 117 92 78 Prcpionlc Acid. 90 Butyrie Acid. 65

Hydrotluoric Acid- 90 120 131 Fluoborlc .Ar-id 170 Fluosilieie A pid 120 Sulphuric Acid. 16 23 23 20 Phosphoric A eid 30 Sulfamic Acid 22 Hydrochloric Acid 260 Sodium Diehrnm at Potassium Qnlnh are Boric Acid Water to make one liber.

l The gures in this table indicate weight in grams.

The various solutions were each employed in carrying out the third step of the typical deburring operation set forth above. The other steps of the operation were carried out, where necessary, with respect to each of the following examples in which only the deburring step is described in detail:

Example 1 Example 2 Solution No. 2 was used for deburring mirror handles manufactured from alloy XXIII. This formula was used in the concentrated form as given in Table II and after an immersion period of 11/2 minutes at 150 F., the parts were free of burrs and then rinsed in water followed by plating with copper, nickel and chrome.

Example 3 Solution No. 3 was used to deburr toy pistols made from alloy XXIII by preparing a bath in which Solution No. 3 was dilutedl to 4 with water and the bath heated to a temperature of 165 F. After a period of 25 to 30 seconds in this bath, the burrs were substantially removed and the parts were rinsed and dried.

Example 4 Solution No. 4 was used to deburr a die casting of alloy XXIII used in an electrical fixture. This casting was satisfactorily deburred by immersion, for a period of 5 minutes, in a bath composed of Solution No. 4 diluted with 5 parts of water with the bath temperature at 100 F.

Example 5 An externally threaded die casting made from alloy XXIII was treated in a bath composed of Solution No. 5 with a one to one dilution with water. The temperature of the bath was maintained at 140 F. and immersion time for removal of the burrs was one minute.

Example 6 Solution No. 6 was used in a bath with a 2 to 1 dilution with water to remove the ash from a die casting of alloy XXIII. The time required was 3 minutes at 150 F. bath temperature.

Example 7 Solution No. 7 was used to remove the grinding burr from a zinc-base die casting of alloy XXV. Solution No. 7 was diluted with 5 parts of water to provide a bath which was maintained at 160 F. After 5 seconds in this bath the burr was removed.

Example 8 Solution No. 8 was found preferable for deburring and cleaning of alloy XXIII die castings. In one instance Solution No. 8 was diluted one to one with water to provide a bath which was held at 145 F. Machining burrs on alloy XXIII parts were removed after immersion of the parts in the bath for 45 seconds.

Preference for this solution is found both in the relative cheapness of the materials used and the lack of criticality as to temperature and time of immersion. This latter point was proven in several other uses of the above bath so long as the bath temperature did not exceed 165 F.

Example 9 Solution No. 9 was used to remove burrs set up by threading allow XXV parts. This solution was diluted one to one with water to provide a bath which was held at F. An immersion time of 11/2 minutes produced a satisfactory deburring of the threads without excessive attack on the threads themselves.

This solution has been found preferable for deburring alloy XXV for essentially the same reasons as Solution No. 8 is preferred for alloy XXIII.

The bath containing Solution No. 9 was also used to deburr a threaded die cast part of alloy XXIII. The same immersion time of 11/2 minutes was satisfactory in removing burrs without any excessive attack on the threads themselves.

Example 10 Solution No. 10 was used to remove the ash and burrs from a lamp fixture manufactured from alloy XXIII. An immersion time of 10 minutes at 60 F. bath temperature was satisfactory in a bath composed of this solution diluted with l0 parts of water.

Example 11 Solution No. 11 was used to remove the burr from a threaded hole in a knob made of alloy XXIII. This solution was used in a bath at a one to one dilution at a temperature of 120 F. with the knob being immersed for a period of 1 minute.

Example 12 Solution No. 12 was used to remove the flash from a horn manufactured of alloy XXIII. This was accomplished in a time of 11/2 minutes at a bath temperature of 110 F. and a bath composed of this solution diluted with 2 parts of water.

Example 13 Solution No. 13 was used to remove the flash from a T square handle made of alloy XXIII. One minute immersion time in a bath at F. and with a one to one dilution of this solution with water gave complete removal of the ash.

Example 14 Solution No. 14 was used to deburr part of an automobile fuel pump of alloy XX[II. This solution was used at one to one dilution to provide a bath at a temperature of 140 F. and the immersion time was 45 seconds.

Example 15 Solution No. 15 with-one to one dilution with water provided a bath which was used to determine the rate of deburring of alloy XXV at 140 and 150 F. T-he figure in the drawing shows a typical die casting burr produced by machining and also in dotted lines the eiect of deburring treatment. Dimensions A and B were measured prior to deburring and are given below in Table III. The same dimensions were measured after immersion in a bath composed of Solution No. 15 diluted with an equal amount of water as indicated above. Immersion time was 2 minutes with a bath temperature of 140 F. Corresponding measurements C and D were made after immersion and are given below in Table III.

TABLE III TABLE IV Before After Loss of Metal Ratio Treatment Treatment A-C F .04695 I: ll n n n .f1-.1308" C .1287 2 E .00105 E '00105 45 B=.1790" D=.1310" B-(D+E)=F=.04695 These results show an even higher rate of metal removal from burrs and sharp edges, the rate being 45 times as great as the rate of removal from flat surfaces and compare with ratio of 5.5 at 140 F. From this, the ratio appears to increase with temperature.

Tables III and IV also give valuable information regarding the rate of attack on at surfaces. This rate is very low, vfor Solution No. 15 it is .000175 inch per minute at 140 F. (this is 1/2 of E in Table III which was for a two minute immersion) and .00105 inch per minute at 150 F. (E in Table IV).

The rates of attack on flat surfaces may be determined for any given solution and used as a handy reference to determine maximum immersion time where the reduction of a particular dimension on a part is critical.

As will be apparent from the above examples the composition of the deburring solution can vary widely between the limits given for the various constituents thereof. Further there is a choice of constituents within the various groups, all of which comes within the scope of our invention. While we have found Solutions No. 8 and No. 9 preferable, other solutions could, under appropriate circumstances become particularly useful and desirable. In this connection we have in mind particularly Solutions No. 10 and No. 11.

In the following claims, it will be remembered that the zinc base alloys are designated by the ASTM numbers as set forth in Table I.

Having thus described the invention what is novel and desired to be secured by Letters Patent of the United States is:

1. A method for deburring zinc-base die castings consisting of treating the die castings with an aqueous acid bath containing, in each 1 to 11 liters in solution, 110 to 350 grams of a chromate radical, 32 to 150 grams of a nitrate radical, 28 to 120 grams of a radical taken from the group of weak acid radicals consisting of borates, formates, acetates, propionates and butyrates, 32 to 180 grams of a radical taken from the group of uorine compounds consisting of uorides, tluoborates and fluosilicates, 16 to 30 grams of a radical taken from the group of strong mineral acid radicals consisting of sulphates, phosphates and sulfamates, at least of the radicals to come from acids and the remainder water, the treatment time being for a period between 5 seconds and 10 minutes at a bath temperature between 60 F. and 165 F. and then rinsing the castings with water.

2. The method as described in claim 3 wherein the zinc base die castings contain more than a trace of copper and further wherein 1 to 260 grams of a chloride radical are added.

3. A method for deburring zinc alloy XXIII die castings including treating the die castings with an aqueous solution containing, in each 2 liters, 270 grams chromic acid, grams nitric acid, 90 grams acetic acid, 131 grams hydrofluoric acid, 23 grams sulphuric acid and the remainder water, the treatment time being for a period between five seconds and l0 minutes at a bath temperature between 60 F. and 165 F., and then rinsing the castings with water.

4. A method for deburring zinc alloy XXV die castings including treating the die castings with an aqueous solution containing, in each 2 liters, 270 grams chromic acid, 46 grams nitric acid, 40 grams acetic acid, 46 grams hydrofiuoric acid, 23 grams sulphuric acid, 200 grams hydrochloric acid and the remainder water, the treatment time being for a period between 5 seconds and 10 minutes at a bath temperature between 60 F. and F., and then rinsing the castings with water.

5. A method for deburring zinc alloy XXIII die castings including treating the die castings in a solution containing, in each 6 liters, 220 grams chromic acid, 115 grams nitric acid, 92 grams acetic acid, 131 grams hydrofluoric acid, 23 grams sulphuric acid, 50 grams sodium dichromate and the remainder water, the treatment time being for a period between 5 seconds and 10 minutes at a bath temperature between 60 F. and 165 F., and then rinsing the castings with water.

6. A method for deburring zinc alloy XXIII die castings including treating the die castings with an aqueous solution containing, in each 2 liters, 270 grams chromic acid, 115 grams nitric acid, 90 grams acetic acid, 131 grams hydroiiuoric acid, 23 grams sulphuric acid and the remainder Water, the treatment time being for a period of 45 seconds at a bath temperature of 145 F and then rinsing the castings with Water.

References Cited in the tile of this patent UNITED STATES PATENTS 2,186,579 Dubpernell et al. Ian. 9, 1940 2,434,021 Thompson et al Ian. 6, 1948 2,497,905 Ostrander Feb. 21, 1950 2,590,927 Brandt et al Apr. 1, 1952 2,613,165 Fischer Oct. 7, 1952 2,760,890 Kosmos Aug. 28, 1956 2,904,414 Ostrander et al. Sept. 15, 1959 

1. A METHOD FOR DEBURRING ZINC-BASE DIE CASTINGS CONSISTING OF TREATING THE DIE CASTINGS WITH AN AQUEOUS ACID BATH CONTAINING, IN EACH 1 TO 11 LITERS IN SOLUTION, 110 TO 350 GRAMS OF A CHROMATE RADICAL, 31 TO 150 GRAMS OF A NITRATE RADICAL, 28 TO 120 GRAMS OF RADICAL TAKEN FROM THE GROUP OF WEAK ACID RADICALS CONSISTING OF BORATES, FORMATES, ACETATES, PROPIONATES AND BUTYRATES, 32 TO 180 GRAMS OF A RADICAL TAKEN FROM THE GROUP OF FLUORINE COMPOUNDS CONSISTING OF FLUORIDES, FLUOBORATES AND FLUOSILICATES, 16 TO 30 GRAMS OF A RADICAL TAKEN FROM THE GROUP OF STRONG MINERAL ACID RADICALS CONSISTING OF SULPHATES, PHOSPHATES AND SULFAMATES, AT LEAST 90% OF THE RADICALS TO COME FROM ACIDS AND THE REMAINDER WATER, THE TREATMENT TIME BEING FOR A PERIOD BETWEEN 5 SECONDS AND 10 MINUTES AT A BATH TEMPERATURE BETWEEN 60*F. AND 165*F. AND THEN RINSING THE CASTINGS WITH WATER. 